Two series of experiments were carried out to invetigate the cerebral hemodynamics in so-called 'netakiri-roujin', old persons who have only few occasions to get up. 1. Acute responses of brain oxygenation during postural change were studied in humans using near infrared spectroscopy. 2. Animal experiments were carried out to observe the time course of cerebral and ocular hemocynamics before, during and after exposure to head-down tilt. Cerebral and ocular blood flow were measured by lase-Doppler flowmetry. Intracranial pressure was measured by a pressure transducer via a catheter inserted into the subarchnoid space or the cisterna magna. Intraocular pressure was measured by both needle insertion technique (invasive) and tono-pen tonometry (non-invasive). The present results suggest :1) Cerebral blood flow increases right after exposure to head-down tilt (-6ﾟC in humans and -45ﾟC in animals), then gradually decreases toward the baseline.2) Increase in intracranial pressure may play a major role in the reduction of cerebral blood flow during the time course of head-down tilt. The elevation of intracranial pressure during head-down tilt is probably due to accumulation of blood in the intracranial veins and shift of cerebrospinal fluid from outside to inside the cranium. Formation of edema is not involved in the acute response of intracranial pressure, but it may further increase the pressure in a chronic stage of head-down tilt.3) Qualitatively similar results are obtained in the ocular circulation, including transient increase in ocular blood flow and sustained elevation of intraocular pressure.Thus, long-lasting bed rest with only few occasions to get up may cause sustained reduction of cerebral blood flow, elevation of intracranial presure, and edema formation which, in turn, possibly affect the brain function.以上の事実より、寝たきり老人の場合、経過が非常に長く、また老齢であることを考慮すると、「寝たきり状態」は慢性的な脳血流減少、頭蓋内圧上昇、脳浮腫発生などを誘起し脳機能低下の一因となることが憂慮される。